JPH04185070A - Simplified measuring device for frequency characteristic in telephone line - Google Patents

Abstract

PURPOSE:To enable the measurement of frequency transmission characteristic of a telephone line in a simple constitution by individually displaying the output level of a facsimile signal passing through a filter passing through on respective high and low frequency sides from among occupied band width of the facsimile signals. CONSTITUTION:A filter group 10 of a frequency characteristic simply measuring device 1 is provided with BPFs 10a and 10b equipped with the passage band characteristic of the prescribed band width with center frequencies f1 and f2. Assuming that the facsimile signal is provided with the frequency of + or -400Hz centered at 1700Hz, the f1 is set to 1300Hz and f2 to 2100Hz. Thus, the transmission level of both terminal frequency of frequency band 1300Hz to 2100Hz is displayed on level display devices 11 and 12. Thus, the frequency characteristic of the telephone line can be easily measured and the adjustment on the facsimile side can be simplified.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a simple frequency characteristic measuring device for telephone lines, and more specifically, for measuring the frequency characteristics of a telephone line installed between a facsimile machine and a telephone office. Display the items that are unique in that they are displayed.

[Prior Art] Recently, facsimile transmitting/receiving devices (hereinafter referred to as facsimiles) that transmit and receive image information via telephone lines have been developed and used. It is used in offices because it can easily transmit information.

FIG. 7 shows the connection status of such facsimile machines, where the telephone office ST and each facsimile machine 100, 100
The telephone line laid between As shown above, the transmission frequencies are fl, fo, f
There is a tendency for the amount of attenuation to increase as the value increases to 2. For this reason, when the amount of attenuation of high frequencies due to the telephone line and L' increases, communication errors occur and the communication baud rate decreases, making it impossible to perform normal communication.

Therefore, with facsimiles, the length of the telephone line is usually assumed to be, for example, about 4 km, and settings are made in advance to compensate for the attenuation of high frequencies due to this length. If such occurrences occur frequently, determine the distance of the telephone line between the facsimile installation location and the central telephone office, and install a semicircular cable installed inside the facsimile machine to compensate for the attenuation of high frequencies on the telephone line of the determined length. It is designed to adjust fixed resistances, etc. However, with such simplified compensation settings, it is not possible to accurately compensate for the attenuation of high frequencies caused by the telephone line, and furthermore, when the length of the telephone line from the facsimile installation location to the telephone office is unknown, For this purpose, it is necessary to connect a measuring instrument such as a spectrum analyzer to the telephone line to determine the frequency characteristics of the telephone line, and then make compensation commensurate with the characteristics. This requires expensive measuring equipment and is time-consuming, so improvements are not possible. It was wanted.

[Problems to be Solved by the Invention] The present invention proposed in view of the above circumstances provides a simple configuration for measuring the approximate frequency characteristics of a telephone line installed between a telephone office and a facsimile installation location. The purpose is to provide a simple frequency characteristic measuring instrument.

[r! Means for Solving Problem R] To achieve the above object, the present invention is proposed to measure the frequency transmission characteristics of a telephone line installed between a facsimile and a telephone office. A filter group including at least a filter that passes a high frequency band and a filter that passes a low frequency band, and a level indicator that individually displays the output level of the facsimile signal that has passed through each of the filters. It is said to be configured with the following features.

In such a preferred embodiment of the present invention, the center frequency of the filter that passes the high frequency band of the occupied frequency band of the facsimile signal and the center frequency of the filter that allows the low frequency band of the facsimile signal to pass are set to The configuration is such that it matches the center frequency for performing compensation adjustment on the low frequency side.

[Function] In the present invention, when a simple frequency characteristic measuring device is connected to a telephone line, the facsimile signal transmitted via the telephone line is filtered through each filter including the high-frequency side filter and the low-frequency side filter of the filter group. , and each filter transmits the facsimile signal of the pass frequency band to a level indicator to display the transmission level of each frequency band. As a result, the approximate frequency transmission characteristics of the telephone line can be determined from the difference in transmission level by I! Therefore, by using this frequency characteristic as a guideline and performing compensation adjustment on the facsimile side, the frequency characteristic can be flattened, and stable facsimile communication can be performed.

[Example〕 The present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram showing an example of the internal configuration of a simple frequency characteristic measuring instrument 1 according to the present invention.
0 is a bandpass filter (hereinafter referred to as B, P, F) with center frequencies f1 and T/f2 10m, 10b
11.12 are B, P, F1, respectively.
Level indicator for displaying output levels of 0a and 10b, 1
3 buffers and amplifies the transmission signal of the telephone line and filters group 1
The buffer amplifier circuit added to 0, TI, and T2 are connection terminals to the telephone line.

FIG. 2 shows the external appearance of the simple frequency characteristic measuring device 1 having such a configuration.The panel surface is provided with level indicators 11 and 12 having a decibel scale, and
A signal input line C is led out from the side of the main body, and clips TI and T2 are provided at the ends of the lines for connection to a telephone line.

Figure 3 shows B and P of such a simple frequency characteristic measuring instrument l.
, Floa, shows the passing frequency characteristics of 10b,
B, P, and Floa are frequencies fl (in this example, 1300
Hz), and B, P, and Flob have a passband characteristic with a predetermined bandwidth as the center frequency, and B, P, and Flob have a frequency f2 (in this example, 2
It has a passband characteristic of a predetermined bandwidth with a center frequency of 100Hz. That is, in this embodiment, assuming that the facsimile signal has a frequency band of ±400H2 centered on 1700Hz,
Approximate frequency characteristics of 00 Hz are obtained by displaying the transmission levels at both end frequencies of the band on level indicators 11 and 12.

FIG. 4 shows an explanatory diagram of an adjustment method for compensating the frequency characteristics of a telephone line using the simple frequency characteristic measuring instrument l of the present invention. 2 is a facsimile machine, facsimile 2 is connected to a telephone line, telephone station ST... and telephone line L"
The facsimile 2' is connected to the calling side's facsimile 2' via the facsimile 2'.

Then, the calling party's facsimile 2' and the nearest telephone office S
It is assumed that the installation distance of the telephone line L' with T is sufficiently short so that attenuation of high frequencies can be ignored, and that the quality of signal transmission between the telephone stations ST and ST is compensated.

The facsimile 2 also includes a compensation circuit section 21 having a low frequency compensation circuit 21a and a high frequency compensation circuit 21b, and the frequency fl (1300Hz) can be adjusted by adjusting the semi-fixed resistor 21b of the low frequency compensation circuit 21a. The transmission characteristic level having a predetermined bandwidth at the center is increased or decreased (Fig. 5(b)).
Reference M), by adjusting the semi-fixed resistor 21d of the high-frequency compensation circuit 21c, the transmission characteristic level having a predetermined bandwidth centered on frequency f2 (2100H2) can be increased or decreased (6th
(see Figure (b)), and a decibel scale indicating an increase or decrease in level is printed on each fixed resistor 21b, 21d.

Next, an adjustment method for compensating for the frequency characteristics of a telephone line using such a configuration will be explained.

■ A facsimile transmission is performed from facsimile 2' to facsimile 2. This facsimile transmission transmits a facsimile signal to the telephone line, and the frequency characteristic simple measuring device l connected in parallel to the telephone line on the facsimile 2 side measures the level. Display 11 shows frequency fl (1300H
In addition to displaying the transmission level 51 (db) of 2), the level display 12 displays the transmission level 52 (db) of the frequency f2 (2100H2).

■Semi-fixed resistor 21b of compensation circuit section 21 of facsimile 2
, 21d are mutually adjusted according to the decibel scale to set the output level of the low-frequency compensation port H21a to be lower than the output level of the high-frequency compensation circuit 21c by (Sl-52)(db).

By making this adjustment, level compensation is performed in the compensation circuit section 21 of the facsimile 2 by the amount that the high frequency is lowered due to the telephone line, so that the signal is transmitted to the modem 22, signal processing section 23, and print output section 24. image signals,
The combined signal transmission characteristics of the facsimile 2 and the telephone line, such as image signals read by the image reading unit 25 and sent to the telephone line side, are flattened, and stable facsimile transmission and reception can be performed.

FIG. 6 is a graph showing the level compensation by the above-mentioned adjustment method with the horizontal axis representing the frequency and the vertical axis representing the signal level. Shows the frequency characteristics of a telephone line. In this frequency characteristic, the output level of frequency f1 is 5l (db), and the output level of frequency f2 is 52 (db). Therefore, as shown in FIG. 5(b), the compensation circuit of facsimile 2 In section 21, the transmission characteristic α with the frequency fl as the center frequency is lowered by (Sl-52)(db) than the transmission characteristic β with the frequency f2 as the center frequency to obtain the synthesized transmission characteristic γ, Equivalently, the transmission characteristic δ shown by the dotted line is determined, and as a result, as shown in FIG. I can get a signal.

As described above, by using the simple frequency characteristic measuring instrument of the present invention, it is possible to easily determine the frequency characteristics of a telephone line, and by making compensation adjustments inside the facsimile according to the determined characteristics, the transmitting and receiving frequency characteristics can be flattened. It becomes possible to

In the above explanation, the case is described in which the adjustment is made by performing facsimile transmission from facsimile 2 to facsimile 2, but this adjustment method is not limited to this method, for example, as shown in FIG. , the frequency characteristic simple measurement II of the present invention is connected to the telephone line L' on the facsimile 2' side, telephones 3 and 3' for communication are provided on the facsimile 2 and 2' sides, and the facsimile is connected from the facsimile 2 to the facsimile 21 side. After transmitting, the semi-fixed resistor 2 of the compensation circuit section 21 on the facsimile 2 side is connected while communicating with the telephones 3 and 39 so that the level display m1ll and 12 of the simple frequency characteristic measuring instrument 1 are at the same level.
It is also possible to perform this by adjusting 1b and 21d.

In the above description, a configuration is described in which two filters are provided, but it is also possible to provide three or more filters, and it is possible to obtain accurate frequency characteristics.

Further, in the above description, a level indicator is provided for each filter, but it is also possible to have a configuration in which the output level of each filter is switched and displayed on one level indicator using a changeover switch. Furthermore, although the configuration is described using an analog display as a level display,
It is also possible to use a digital display - [Effects of the Invention] As can be understood from the above explanation, according to the present invention, it is possible to easily measure the frequency characteristics of a telephone line with a simple configuration and at low cost. Since a measuring device can be provided and compensation adjustments can be made on the facsimile side in accordance with the measurement results using this simple measuring device, it is possible to easily make adjustments when installing the facsimile.

[Brief explanation of drawings]

Fig. 1 is an example of the block configuration of the simple frequency characteristic measuring instrument of the present invention, Fig. 2 is its external view, Fig. 3 is a frequency characteristic diagram of its filter group, and Fig. 4v! J is an explanatory diagram when performing facsimile frequency compensation adjustment using the simple frequency characteristic measuring instrument, Figures 5 (a) to (C) are explanatory diagrams of changes in frequency characteristics due to the adjustment, and Figure 6 is an explanatory diagram of facsimile frequency compensation adjustment using the simple frequency characteristic measuring instrument. FIG. 7 is a connection diagram for conventional facsimile transmission and reception, and FIG. 8 is a diagram showing the frequency characteristics of a telephone line. Explanation of C code... Frequency characteristic simple measuring instrument 101 @ filter group 10a, 10b*s* filter 11.12φ/φ level indicator 2...Facsimile L building...Telephone line ST...Telephone office

Claims (1)

[Claims] (1) In order to measure the frequency transmission characteristics of the telephone line installed between the facsimile and the telephone office, a filter that passes the high frequency band and a filter that passes the low frequency band of the frequency band occupied by the facsimile signal. A simple frequency characteristic measuring device for a telephone line, comprising: a filter group including at least the following; and a level indicator that individually displays the output level of a facsimile signal that has passed through each of the filters.